1. Field of the Invention
The present invention relates to a method of cutting prepreg that is used for manufacturing a laminated plate.
2. Description of the Background Art
Prepreg is formed into an elongated shape through the following processes: an elongated base member such as glass cloth or paper is impregnated with a varnish of a thermosetting resin; and heated and dried so that the thermosetting resin is semi-set. The dried prepreg is cut along a length direction and in a width direction orthogonal to the length direction into a rectangular shape that has a constant dimension. The cut prepreg is next applied. For example, a plurality of sheets of prepreg cut as described above are superposed with both of the surfaces of each sheet covered with copper foil, etc. The superposed sheets are heated and pressed to form a molded product. Thus, a copper-clad laminate is manufactured.
When cutting prepreg in the manner described above, a cutting blade, such as a guillotine, a rotary cutter, a shirring blade or a saw blade, is used. However, since the prepreg is formed by a fragile semi-set resin adhering to a base member, the cutting process tends to generate cutting dust of the resin and the base member. The cutting dust is scattered around to cause degradation in the work environment. Furthermore, the cutting dust tends to adhere to the prepreg and to be mixed into the molded product or affixed thereon as foreign matter when molded in the next process with the copper foil. In recent years, there have been increasing demands for high-density circuit patterns that are very sensitive to foreign matter. Thus, there have been strong demands for the prevention of the generation of cutting dust that is introduced into the work environment.
In order to solve this problem, a method has been proposed in which a portion of prepreg to be cut is heated by an infrared heater and thereby softened. The prepreg is cut at the softened portion so that it is possible to prevent the generation and scattering of cutting dust. However, when the prepreg is heated by an infrared heater as mentioned above, portions other than the portion of the prepreg to be cut are also widely heated with the result that the prepreg resin in the heated portions may set, resulting in degradation in the quality.
Moreover, as disclosed in Japanese Laid-Open Patent Application No. 3-94988, another method in which a laser light beam is used to cut prepreg has been proposed. In this method, the prepreg is cut not by a shearing force, etc., but by a burning process of a laser light beam. Therefore, the prepreg can be cut without generating cutting dust. However, in this method, both the base member and the resin need to be simultaneously cut by using a laser light beam. Thus, when the base substrate is made of glass fibers, it is necessary to use a laser light beam with high output power. The resulting problem is that the resin is carbonized due to irradiation of the high-power laser light beam, resulting in degradation in the quality.
The present invention has been devised to solve the above-mentioned problems, and its objective is to provide a method of cutting prepreg which eliminates the necessity of applying a heating process, etc., to portions other than a portion of the prepreg to be cut, and which can also prevent the generation of cutting dust when cutting.
According to an aspect of the present invention, a method of cutting prepreg that has been formed by impregnating a base member with a resin and semi-cured into a predetermined dimension, is provided. The method includes directing a laser light beam onto a surface of the prepreg to soften the resin of the portion irradiated by the laser light beam, and cutting the softened portion of the resin with a cutting blade. With this arrangement, the cutting blade cuts the softened portion of the prepreg resin so that it becomes possible to prevent the resin from scattering as cutting dust when cutting with the cutting blade.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein the laser beam is directed to the prepreg with an irradiation position being fixed while the prepreg is being fed (transferred) so that the prepreg resin of the portion irradiated with the laser beam is heated and softened. Furthermore, the softened portion of the prepreg is cut by a cutting blade that is placed forward of the irradiation position with respect to the feeding direction of the prepreg. With this arrangement, the prepreg resin is heated and softened at the portion irradiated with the laser light beam, and cut by a cutting blade that is placed forward of the irradiation position in the feeding direction. Therefore, it is not necessary to shift the position of the laser light beam and the cutting blade. Moreover, as the prepreg is transferred, the portion at which the resin is heated and softened by the irradiation of the laser light beam is cut so that the generation of cutting dust due to the cutting process is prevented.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which the irradiation position of the laser light beam is shifted when irradiating the surface of the prepreg. Thus, it is possible to freely shift the cutting position.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which the cut end portion of the prepreg is irradiated with a laser light beam after being cut by the cutting blade. With this arrangement, the laser light beam further softens and fuses the cut end portion of the prepreg so that the prepreg forms a smooth face. Thus, resin dust is prevented from coming off the cut end face of the prepreg.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which a laser light beam is fixed with respect to the portion of the prepreg cut by the cutting blade while the prepreg is being transferred. With this arrangement, the irradiation positions of the laser light beam and the cutting blade do not have to be shifted. Furthermore, as the prepreg is transferred, the cut portion of the prepreg can be heated so that resin dust is prevented from coming off the cut end face of the prepreg.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which a carbon oxide gas laser is used as the laser light beam. With this arrangement, by properly selecting the output of the carbon oxide gas laser, it is possible to heat and soften the prepreg resin without causing carbonization thereof.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which the cutting blade comprises upper and lower rotary blades with at least the lower rotary blade being driven to rotate. With this arrangement, the rotation of the rotary blades can be controlled depending on the state of the prepreg.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which a reflection mirror is placed on a light path of a laser light beam emitted from a laser oscillator so that a laser light beam is reflected by the reflection mirror to a predetermined irradiation position of the prepreg. With this arrangement, by changing the number, the positions and the angles of one or more reflection mirrors, the irradiation position of the laser beam is easily adjusted without requiring a change of the position of the laser oscillator.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which a light-converging lens is placed at an outlet that outputs the reflected laser light beam from the at least one reflection mirror so that the laser light beam that has passed through the light-converging lens is directed onto the prepreg. With this arrangement, even when the distances of the light paths from the laser oscillator to the irradiation positions of the laser light beam on the prepreg increase, it is possible to correct a widened laser light beam by allowing it to pass through the light-converging lens, and thereby reduce the deviations of the laser light output that is directed to the prepreg.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein reflection mirrors are placed at positions forward and rear of a cutting blade along the light path of a laser light beam from the laser oscillator, with the reflection mirror on the side closer to the laser oscillator able to shift to a position out of the light path of the laser light beam from the laser oscillator. With this arrangement, the prepreg may be cut with the cutting blade at the portion that has been softened by the irradiation of the laser light beam, even when the transfer direction of the prepreg varies.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein a partial reflection mirror that transmits one portion of directed laser light beam and that reflects the other portion to the prepreg, as well as a total reflection mirror that reflects the laser light beam that has passed through the partial reflection mirror to the surface of the prepreg, are placed on the light path of the laser light. Furthermore, of the laser light beam reflected by the partial reflection mirror and the laser light beam reflected by the total reflection mirror, one is directed to the prepreg at the forward position in the advancing direction of the cutting blade and the other is directed to the cut end face of the prepreg. With this arrangement, it is possible to direct the laser light beam to the prepreg at the position forward, in the advancing direction of the cutting blade, as well as at the position to the rear thereof, using a single laser generator.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein the partial reflection mirror and/or the total reflection mirror and the cutting blade are movably and integrally formed as a single unit. With this arrangement, as the cutting position shifts, the laser generator can direct the laser light beam relative to the cutting position of the prepreg to be cut by the cutting blade.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein a partial reflection mirror that reflects one portion of the laser light beam and that transmits the other portion and a total reflection mirror for totally reflecting the laser light beam that has passed through the partial reflection mirror are placed on the light path of the laser light beam from the laser oscillator. One of the reflected laser light beams is directed to a position at a rear of the cutting blade in the prepreg feeding direction so as to soften the prepreg resin, with the other being directed to the cut portion at a position forward of the cutting blade in the prepreg feeding direction. With this arrangement, the laser light beam from a single laser oscillator is split and directed to a forward position as well as a position to the rear of the cutting blade so that it is possible to reduce the number of laser oscillators and consequently to reduce the installation costs.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein laser light beams emitted from a plurality of laser oscillators are converged and directed to the prepreg. With this arrangement, the output of the laser light beam from each laser oscillator is lower, reducing hazards associated with the device.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein the laser light beam is directed to the prepreg with its focal point offset from the surface of the prepreg. With this arrangement, the surface temperature of the prepreg to be irradiated and the spot diameter of the laser light beam can be easily controlled so that it is possible to adjust the energy of the laser light beam on the surface of the prepreg, and consequently to prevent the prepreg resin at the irradiated portion from being carbonized.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein the laser light beam, emitted from the laser oscillator, passes through an optical fiber, and is directed to a predetermined irradiation position of the prepreg. With this arrangement, it becomes possible to easily adjust the irradiation position of the laser light beam by adjusting the tip position of the optical fiber, without requiring a change in the position of the laser oscillator.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement in which the temperature of the prepreg at the irradiation position of the laser light is detected, and based upon this detected temperature, at least one of the output of the laser light beam from the laser oscillator and the transporting speed of the prepreg is adjusted. With this arrangement, when the detected temperature is low, a feed-back controlling operation for increasing the output of the laser light beam and for decreasing the transporting speed of the prepreg is carried out, and when the detected temperature is high, a feed-back controlling operation for reducing the output of the laser light beam and for increasing the transporting speed of the prepreg is carried out. Thus, the prepreg resin is consistently heated at an optimal temperature and cut in a softened state.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein a partial reflection mirror that reflects one portion of the laser beam and transmits the other portion thereof and a total reflection mirror that totally reflects the laser light beam that has passed through the partial reflection mirror are placed on the light path of the laser light beam from the laser oscillator in the width direction orthogonal to the feeding direction of the prepreg so that the reflected laser light beams are respectively directed to the prepreg. With this arrangement, the laser light beam from a single laser oscillator is split and directed to a plurality of portions, in the width direction of the prepreg, so that the resin is simultaneously softened at a plurality of portions in the width direction of the prepreg and the prepreg can be cut simultaneously at a plurality of positions in the feeding direction.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein a plurality of partial reflection mirrors are placed on the light path of the laser light beam, with the respective partial reflection mirrors shifting between positions on the light path of the laser light beam and positions out of the light path, so that the laser light beams reflected by the partial reflection mirrors positioned on the light path of the laser light beam are directed to the prepreg. With this arrangement, the positions and the number of branches of the laser light beam from the laser oscillator can be changed by shifting the partial reflection mirrors so that the cutting positions of the prepreg and the number of cuts can be easily changed.
According to a further aspect of the present invention, the method of cutting prepreg has an arrangement wherein a plurality of partial reflection mirrors are placed on the light path of the laser light beam and a shutter is placed on an outlet through which each of the reflected laser lights of the partial reflection mirrors is output, so that laser light beams reflected by the partial reflection mirrors with the shutters open are directed to the prepreg. With this arrangement, the positions and the number of the branches of the laser light beam from the laser oscillator can be changed by opening and closing the shutters so that the cutting positions of the prepreg and the number of cuts can be easily changed.
According to a further aspect of the present invention, a prepreg cutting apparatus is provided. The prepreg cutting apparatus cuts prepreg formed by impregnating a base member with a resin and semi-curing the impregnated base member. The prepreg cutting member includes a laser light source that emits a laser light beam that is directed onto a surface of the prepreg to soften the resin of the portion irradiated by the laser light beam, and a cutting instrument that cuts the softened portion of the resin with a cutting blade.
According to a further aspect of the present invention, a prepreg cutting apparatus includes a first reflection mirror that reflects a laser light beam to a first portion of prepreg. Resin of the first portion of prepreg is heated by the laser beam. As a result of the heating of the prepreg, dust is prevented from being generated when the prepreg is cut by the prepreg cutting apparatus.
According to a further aspect of the present invention, a prepreg cutting apparatus includes a partial reflection mirror that reflects a first portion of a laser beam from a laser light source to a second portion of prepreg. The partial reflection mirror also transmits a second portion of the laser beam to the first reflection mirror. The partial reflection mirror can be used to split a laser light beam and thereby provide two laser light beams that can be applied to different portions of a prepreg.
According to a further aspect of the present invention, a prepreg cutting apparatus includes a light-converging lens that converges a laser light beam reflected from a first reflection mirror. The light-converging lens can be used to converge or widen a laser light spot on a portion of prepreg irradiated by a laser light.
According to a further aspect of the present invention, a prepreg cutting apparatus includes a cutting blade, a first reflection mirror and a second partial reflection mirror that are integrally and movably formed as a single unit. As a single unit, the cutting apparatus can move elements in a same direction at a same movement speed.